If a tenant is only there a month so far and its month to month no security dep...?

the first month they are short 200 dollars which i said was ok due to their situation... then this next month comes along they are short 400....so i stated they needed full amount by the 1st or they can leave.. they said they would be out by friday this friday april 2nd...and adv they needed 2 more weeks..told them needed to pay for it.. they didnt want to pay anything and said i had to give 30 days notice... is this true ? even though they said they would be 400 short ????